As shown in FIG. 8, a conventional digital radio terminal is generally composed of an RF portion 80, an AFE (Analog Front End) portion 90, and a DBB (Digital Base Band) portion 100. The RF portion 80 has an antenna 81, a transmission amplifier portion 82 and a receiving amplifier portion 83 respectively including a mixer, a power amplifier, and so on, and a duplexer circuit 84.
Besides, the AFE portion 90 converting a signal into analog-digital mutually is composed of a receiving portion and a transmission portion, and has a receiving filter 91, a receiving ADC (Analog-Digital Converter) 92, a transmission DAC (Digital-Analog Converter) 93, and a transmission filter 94. The DBB portion 100 performing a digital signal process has a signal processing portion 101.
In a radio terminal shown in FIG. 8, an analog signal received at the antenna 81 is amplified and so on at the receiving amplifier portion 83, and thereafter, a filter process is performed at the receiving filter 91. Further, the filter processed analog signal is converted into a digital signal by the ADC 92, to be supplied to the signal processing portion 101.
Besides, the digital signal to be transmitted, outputted from the signal processing portion 101 is converted into an analog signal by the DAC 93, and thereafter, the filter process is performed at the transmission filter 94. Further, a predetermined process such as an amplification is performed at the transmission amplifier, and thereafter, it is transmitted via the antenna 81.
Here, when the radio terminal corresponding to two radio methods is constituted, it is generally constituted so that two circuits corresponding to one radio method shown in FIG. 8 are disposed in parallel as shown in FIG. 9. Incidentally, in FIG. 9, the same numerals and symbols are used for a block and so on having the same function with the block and so on shown in FIG. 8. In FIG. 9, an RF-A80, an AFE-A90, and the signal processing portion 101 connected to the AFE-A90 is corresponding to one radio method, and an RF-B80, an AFE-B90, and the signal processing portion 101 connected to the AFE-B90 is corresponding to another radio method.
Besides, as a constitution of the radio terminal corresponding to plural radio methods, there are the one in which a broad-band filter and a low-band filter are switched in accordance with the radio method (for example, refer to Japanese Patent Application Laid-open No. Hei 10-224243 (Patent Document 1)), the one in which a band width is changed by changing a sampling frequency of a digital filter (for example, refer to Translated National Publication of Patent Application No. 2002-500490 (Patent Document 2)), the one in which a filter is changed by a switching of softwares to change the band width (for example, refer to Japanese Patent Application Laid-open No. 2000-13279 (Patent Document 3)), and so on.
However, when the radio terminal is constituted as shown in FIG. 9, the number of parts constituting the radio terminal becomes very large, and a miniaturization of the radio terminal becomes difficult because an area required for mounting the parts increases. Besides, a cost necessary for manufacturing (parts cost and so on) becomes expensive.
As a method intending to reduce the number of parts and miniaturize the radio terminal with respect to the constitution shown in the FIG. 9, a constitution in which the AFE portion and the DBB portion are shared with two radio methods, is conceivable. However, requested characteristics in accordance with the radio methods (damping characteristics of the transmission/receiving filters, operating frequencies and resolution performances of the ADC and the DAC, and so on) are different, and therefore, it is necessary to use the filter, the ADC, and the DAC agreed with the highest specification among the radio methods when the AFE portion is shared.
Consequently, when a circuit is shared, electric power is wasted because it is operated with a performance more than required depending on the radio method operated actually. Besides, there is a case when the damping characteristics of the filter become insufficient depending on the selected radio method, and a further digital filter process may be required depending on the radio method to thereby waste electric power.
[Patent Document 1] Japanese Patent Application Laid-open No. Hei 10-224243
[Patent Document 2] Translated National Publication of Patent Application No. 2002-500490
[Patent Document 3] Japanese Patent Application Laid-open No. 2000-13279